This revised shared instrument grant application requests funds to purchase a state-of-the-art matrix-assisted laser desorption/ionization hybrid quadrupole time-of-flight mass spectrometer (MALDI-QTOF MS). The current MALDI-TOF instrument will be decommissioned in 2003. A group of 16 NIH-funded researchers will be the major users of the requested instrumentation, and 12 other users will use the instrument for projects that are not currently NIH-funded. We estimate that a minimum of 250 samples will be analyzed per week, and that MS/MS data will be needed for the majority of those samples. A significant new development in Memphis is the new UTHSC Cancer Institute. The Boston-Baskins Cancer Group has entered into a partnership with UTHSC. A temporary director has been hired, an NIH NCI P21 planning grant has been submitted (March, 2003), a permanent director will be hired, two new buildings will be constructed, and new faculty will be hired. Dr. Desiderio will direct the UT Cancer Institute Proteomics Laboratory. Many more researchers will be hired, and many will need a MALDI QTOF MS for their research programs. Many investigators from various disciplines have been using our rapidly aging MALDI-TOF instrument, and they have extensive experience with the sample preparation methods for MALDI and with the interpretation of MALDI data. Advantages of the requested instrument include the ability to prepare samples before instrument time, the ability to reanalyze samples whenever necessary, and (very important) the user-friendliness of the instrumentation. It is significant to note that our users operate the MALDI-TOF instruments. The users of our aging MALDI-TOF mass spectrometer are acutely aware of its rapidly decreasing performance in terms of sensitivity and mass accuracy, and of its lack of sequencing capabilities. Therefore, we will remove our MALDI -TOF MS from service in 2003. Often, experiments must be repeated because the MALDI-TOF analysis has failed, or because amino acid sequence data are necessary - but cannot be obtained with the MALDI-TOF. Clearly, a state-of-the-art MALDI-based mass spectrometer with MS/MS capabilities is needed to support the rapidly increasing number of extensive and diverse research programs on the UTHSC campus.